VANCOUVER - The federal government has again rejected a proposed $1.5-billion, open-pit, gold-copper mine in British Columbia's Interior over environmental concerns, a decision critics are celebrating but one the company vows to fight.

Environment Minister Leona Aglukkaq said Wednesday evening that her ministry has rejected the New Prosperity Gold Copper Mine for a second time because it will cause significant adverse environmental effects that can't be mitigated.

Just four years ago, the ministry rejected the project because Taseko Mines Ltd. (TSX:TKO) planned to drain a lake to use as a tailings pond.

"The Government of Canada will make decisions based on the best available scientific evidence while balancing economic and environmental considerations," said Aglukkaq in a news release.

"The government will continue to make responsible resource development a priority and invites the submission of another proposal that addresses the government's concerns."

Aglukkaq said in making the decision, the federal government considered and agreed with the conclusions of an report released by the Independent Review Panel on Oct. 31, 2013.

That report found the project would cause "significant adverse effects" on water quality, fish and fish habitat in a lake of significance to area First Nations.

The site is 125 kilometres southwest of Williams Lake, B.C., and is the tenth largest undeveloped gold-copper deposit in the world.

Following the report's release, Taseko applied to the Federal Court for a judicial review of the assessment, arguing the panel used the wrong information in drawing its conclusions.

Brian Battison, vice-president of corporate affairs at Taseko, said the company is "terribly disappointed," but added Wednesday's announcement is not the end of the project because it's too important for British Columbians and residents of a region known as the Cariboo.

"We're going to continue with our existing judicial review, which is currently before the courts," he said. "That will continue to run its course, and consideration will be given to what other course of action may be available to us."

Asked if the company would submit another proposal, Battison replied, "I'm not saying we won't, but we've been down that road before." He said the process has cost the company millions of dollars.

Battison said the decision will be "tough news" and a "shock of disappointment" for the thousands of Cariboo residents who have supported the mine.

"It's a significant event in the life of mining in British Columbia, and it will have a profound effect on the attitude investors have towards the province," he added.

But Tsilhqot'in Tribal Chairman Joe Alphonse said members are excited about the announcement, which was big news to the community, and it's time to celebrate. He said he's no longer worried about the project moving forward.

"I think if you've had two scathing reports like this come out, you know, I think that speaks volumes about any possibility of moving forward on this project by anyone," he said. "So we have comfort in that."

Alphonse said certain areas should remain untouched, like Fish Lake, but the Tsilhqot'in have been developing their own mining policy.

"We would be open to mining proposals if companies come to our door, work with us, treat us with respect and allow us to develop proposals together," he said. "In today's day and age, projects like this aren't going to go through unless all parties are working together."

The Sierra Club BC also welcomed the announcement, saying the decision was the only one the federal government could make.

"Even as we are celebrating this important moment, we are mindful of how long and onerous the process has been for all players – government, First Nations and concerned citizens," said executive director Bob Peart in a news release.

"For such an obviously destructive project to be considered again and again through three separate processes over nearly a decade, is not a good use of resources that could be devoted to projects that bring community and environmental benefits."

The City of Williams Lake said it would respond to the decision on Thursday morning.